1. Field of the Invention
The present invention relates to a method of manufacturing a fin-tube heat exchanger which is suitably used as an evaporator of a refrigerator, show case or the like.
2. Description of the Prior Art
Heat exchangers of so-called fin-tube type are used in refrigerators, show cases and so forth. Generally, in such type of heat exchangers, plate fins are arranged at a predetermined pitch in the direction of air flow, i.e. in the direction of a row of the fins, while refrigerant pipes are arranged in an alternating or staggered manner in the direction of rows of the plate fins, so as to attain a boundary layer front edge effect and turbulence promotion effect thereby to improve the capability of the heat exchanger. This type of heat exchanger is shown, for example, in U.S. Pat. No. 3,381,494.
In the manufacture of such fin-tube heat exchangers in which plate fins in a row are arranged in non-alignment with plate fins in adjacent rows and straight portions of refrigerant pipe are arranged in a staggered manner as viewed in a direction of air flow, the plate fins and straight portions of refrigerant pipe are assembled together and then U-bends or return bends are connected by brazing to the ends of lengths of straight pipe so as to permit a refrigerant to flow in a zigzag manner. Thus, in terms of manufacture, such heat exchangers are not favorable due to the necessity of brazing work and inspection after the brazing and yet the fraction defective is considerably high.
On the other hand, such a heat exchanger having a continuous length of refrigerant pipe bent in a zigzag manner without the use of lengths of pipe having U-bends is known. The method of manufacturing this type of heat exchanger is disclosed in U.S. Pat. No. 2,156,538 or Japanese Patent Publication No. 29606/1981. By way of example, the manufacturing method as shown in Japanese Patent Publication No. 29606/1981 will be explained hereinunder with reference to FIGS. 1 to 4. A plate fin 1 is formed provided, at positions spaced equidistantly away from its upper and lower edges, with two pipe-receiving holes 3 for passing therethrough a length of refrigerant pipe 2. These plate fins are placed in fin-receiving grooves 4 which are formed at a predetermined pitch in a fin positioning fixture 5. More specifically, the plate fins 1 are of the same shape and are placed in the fin positioning fixture 5 in a manner shown in FIG. 1. Namely, a predetermined number of plate fins 1 (five fins in this case) are placed into every other groove 4 at a pitch designated at 6 and then, leaving out a predetermined number of grooves 4 (four grooves in this case) to provide that portion of the pipe which is bent to form U-bends, a predetermined number of plate fins 1 (nine fins in this case) are placed in the grooves 4 at the pitch 7 of the grooves 4. Then, leaving out a predetermined number of the grooves 4 to provide that portion of the pipe which is to be bent, the plate fins 1 are placed in respective grooves 4. Thus, the plate fins 1 are arrayed on a straight line. Subsequently, the refrigerant pipe 2 is inserted into the pipe receiving holes 3 of the plate fins 1 and is then expanded by inserting a tube expander, so that it is in close contact with the plate fins 1. Subsequently, the assembly of the refrigerant pipe 2 and the plate fins 1 is removed from the fixture 5 and is arcuately bent as at portions 8 (see FIG. 3) to make the refrigerant pipe 2 zigzag-shaped. Consequently, the plate fins 1 are arranged in parallel rows with gaps 9 between the adjacent rows. In the manufacture described above, the refrigerant pipe 2 is necessarily arranged to form squares in section transverse to the axial direction of the pipe since the plate fins 1 are lined up in the fin positioning fixture 5. Namely this manufacturing method is disadvantageous in that a staggered pipe arrangement which offers a high performance of the heat exchanger cannot be realized.